Notice how Calc inserted outline controls around our spreadsheet. There are also numbers in the outline area. These numbers represent levels of grouping in the subtotaled worksheet.

Clicking on the number 1 shows the highest level of subtotal calculation, the grand total.

Level 2 shows us the next level down. The category subtotals.

And finally level 3 shows us the individual sales transactions.

The plus and minus icons in the outline area will let you collapse and expand the groupings as you wish.

If you want to turn off the outline feature, select outline from the data menu then select remove.